1. Field
This disclosure relates generally to lead frames for packaged electronic devices, and more specifically, to a lead frame with a flag having in-plane and out-of-plane encapsulant mold compound locking capability.
2. Related Art
Electronic devices such as integrated circuits and systems on a chip can be implemented in packaged electronic devices. The elements of a packaged electronic device generally include one or more metal lead frames, one or more integrated circuit die, bonding material to attach the integrated circuit die to a flag (or die pad) of the lead frame, bonding wires which electrically connect pads on the die to individual leads of the lead frame, and a hard plastic packaging material, or encapsulant, which covers the other components and forms the exterior of the packaged electronic device. The packaging material, or encapsulant, provides protection from hostile environments and can provide structural support for electrical interconnections from the die.
The lead frame is the central supporting structure of such a package. A portion of the lead frame is internal to the package and completely surrounded by the packaging material. Portions of the leads of the lead frame may extend externally from the package and can be used to connect the package externally. A quad flat no leads (QFN) package is an example of an integrated circuit package usable with surface mounted printed circuit boards. In this type of integrated circuit package, the leads do not extend externally from the package. Rather, lead contacts of the lead frame are exposed on the bottom surface of the package for connection to the outside complements. As such, the lead frame used in a QFN integrated circuit device is sometimes referred to as a leadless lead frame.
One potential drawback of some packaged devices is that certain environmental stresses can cause separation, or delamination, of portions of the lead frame (e.g., the flag) from the packaging material. For example, reflow soldering is a common process for attaching surface mounted components such as a QFN packaged electronic device to a circuit board. During reflow soldering, the packaged electronic device can be subjected to elevated temperatures (e.g., 260° C.). Stress in the package due to differences in thermal expansion and other material properties of the dissimilar materials used in packaging under heat can result in separation. Temperature stresses can also be caused by normal operational variations in temperature. For example, packaged semiconductor devices used in automotive applications often experience operating environment temperatures from about 50° C. to about −40° C.
Different encapsulant mold compounds exhibit better performance characteristics for various operating environments (e.g., glass-like compounds), but some of those compounds may also exhibit greater risk of separation from encapsulated lead frames and devices. Since separation of a lead frame from the packaging material during manufacture or under operating conditions can adversely affect operation of the packaged electronic device, it is desirable to provide a lead frame having features that enhance locking of the lead frame with the molding material.
The use of the same reference symbols in different drawings indicates identical items unless otherwise noted. The figures are not necessarily drawn to scale.